1. Field of the Invention
The present invention relates to a package structure for a hybrid optical module in which components of an optical pickup, excluding an objective lens are to be mounted, and also a method of producing it.
2. Description of the Related Art
Among devices constituting a CD player, an optical pickup which detects an optical signal is the heart of the CD player. With respect to such an optical pickup, requests for a reduced cost, a high reliability, and a reduced weight have been given. However, a conventional optical pickup which is configured by discrete components cannot meet such requests. Therefore, optical modules of a hybrid configuration which are called a hologram pickup or a laser coupler have begun to be used.
In such hybrid optical modules, particularly in a laser coupler, all parts other than an objective lens are integrated into one component, so as to extremely reduce the size of the module. Specifically, a photo diode IC substrate on which an optoelectric converting element is formed is used as a base, and a prism and a laser diode are mounted on the base, thereby configuring a laser coupler. The laser coupler is housed in a package which is not shown. An optical lens and mechanical parts such as an actuator are placed on the package to complete an optical pickup unit.
The package into which parts constituting the hybrid optical module are housed is made of a metal including ceramics, or a resin. The latter material is light in weight and suitable for miniaturization, but is inferior in mechanical strength and heat radiation property than a metal. A process of producing a hybrid optical module includes a heat treatment step in which the temperature is raised to a range of 180 to 200° C. Since the temperature range is immediately below the melting point of a plastic, the mechanical strength of a plastic is expected to be lowered.
In some cases, a plurality of laser devices which are used as light sources of a hybrid optical module of this kind are bonded onto a metal frame. When a laser device is to be die-bonded onto a metal frame, a heat treatment is conducted. The metal frame onto which a laser device is to be die-bonded is shared among the plural laser devices. During a process of die-bonding one laser device, therefore, the die-bonding state of another laser device may be adversely affected. In this case, misalignment of the optical axis is caused by heat applied in the process of die-bonding.